With the fossil fuel is drying up after being exploited for several decades and also considering the strategy of sustainability and environmental protection, there are more and more researches focusing on the development of solar energy. However, since the high-efficiency silicon wafers that are available today are still can not provide satisfactory electrical performance and are very expensive, the levelized cost of electricity for any solar electric generating system is higher than other power generating sources, such as thermal power plants or nuclear power stations. Thus, despite of its promising future, the use of solar cells is still limited. Responsively, in order to reduce the power generating cost, the technology of thin-film solar cell (TFSC) is getting more and more attention since the thin-film solar cells can be made by materials that are significantly cheaper, and the development in thin-film solar cell technology is focusing most on how to effectively reduce the cost of the light absorption layer in solar cells while maintaining a high power conversion efficiency. For effectively enhancing the conversion quantum efficiency inside solar cells and the solar absorptivity, a variety of structures, including light-trapping structures and grating structures, had been developed to be built inside thin-film solar cells, and consequently by the light scattering enabled by those light-trapping structures, light entering a thin-film solar cell can be reflected and refracted multiple times between solar panels inside the thin-film solar cell while allowing the same to be absorbed by the absorption layers, and thus enabling the solar photovoltaic conversion efficiency to be enhanced.
Recently, a number of researchers had been focusing their studies to the integration of silver nanostructures into solar cells for experimenting an innovated light trapping method in thin film solar cell by the use of metallic nanostructures that supports surface plasmon resonance (SPR). SPRs, especially localized SPRs, are collective electron charge oscillations in metallic nanoparticles that are excited by light. It is noted that nanoparticles of noble metals exhibit strong absorption bands in the specific regime of solar spectrum, and this extraordinary absorption increase has been exploited to increase light absorption in photovoltaic cells by depositing metal nanoparticles on the cell surface. Since the excitation of plasmon resonances can capture and trap the sunlight into the active layer and increase absorption strength, many light trapping techniques of different silver nanostructure have been investigated in thin film solar cell applications for increasing light absorption, and thus increasing photoelectric conversion efficiency.
More recently, there are many metallic nanostructures engineered within the solar cell geometry for confining and folding light into the ultrathin active layer, and thereby increasing light absorption. For example, a kind of novel thin film solar cell design of introducing nano-gratings onto metallic back contact of thin film solar cells has been investigated widely since experimentally it can enhance the desired light confining effect by five times. Nevertheless, such nano-gratings are difficult to manufacture, especially in large area. Other than that, there are other ideas of light confining structure being proposed for increasing conversion efficiency of thin film solar cells, and most of those light confining structures are made of dielectric materials. However, while intending to made such light confining structures using other materials, such as precious metals, the situation is completely different both in design and manufacturing points of view.
There are already many researches relating to the use of metallic nanostructures in thin film solar cells. One of which is a paper disclosed in 2008, entitled “Absorption enhancement in solar cells by localized Plasmon polaritons”, by Dr. Carsten et al., in which an investigation is provided to enhance the absorption in solar cells by employing localized plasmon polaritons excited in silver nanowires, whereas the solar cells are assumed to be made of amorphous silicon. In another paper disclosed in 2010, entitled “Effective light trapping in polycrystalline silicon thin-film solar cells by means of rearlocalized surface plasmons”, by Quyany et al., in which significant short-circuit current enhancement of 29% has been achieved for evaporated solid-phase-crystallized polycrystalline siliconthin-filmsolar cells on glass, due to light trapping provided by Agnanoparticles located on the rear siliconsurface of the cells.
Moreover, there is further a paper disclosed in Nature Materials at 2010, entitled “Plasmonics for improved photovoltaic devices”, in which recent advances at the intersection of plasmonics and photovoltaics are surveyed and an outlook on the future of solar cells based on these principles is offered. Notably, although design approaches based on plasmonics can be used to improve absorption in photovoltaic devices, permitting a considerable reduction in the physical thickness of solar cells in small size, their usability in large-size solar cells is still questionable as well as its commercialization possibility in the future.